Re: [Qemu-devel] [PATCH 11/14] hw/vfio/ccw: avoid taking address members in packed structs

[Thomas Huth <thuth@redhat.com>]

On 02/04/2019 18.00, Cornelia Huck wrote:
> On Fri, 29 Mar 2019 11:11:01 +0000
> Daniel P. Berrangé <berrange@redhat.com> wrote:
> 
>> The GCC 9 compiler complains about many places in s390 code
>> that take the address of members of the 'struct SCHIB' which
>> is marked packed:
>>
>> hw/vfio/ccw.c: In function ‘vfio_ccw_io_notifier_handler’:
>> hw/vfio/ccw.c:133:15: warning: taking address of packed member of ‘struct SCHIB’ may result in an unaligned pointer value \
>> [-Waddress-of-packed-member]
>>   133 |     SCSW *s = &sch->curr_status.scsw;
>>       |               ^~~~~~~~~~~~~~~~~~~~~~
>> hw/vfio/ccw.c:134:15: warning: taking address of packed member of ‘struct SCHIB’ may result in an unaligned pointer value \
>> [-Waddress-of-packed-member]
>>   134 |     PMCW *p = &sch->curr_status.pmcw;
>>       |               ^~~~~~~~~~~~~~~~~~~~~~
>>
>> ...snip many more...
>>
>> Almost all of these are just done for convenience to avoid
>> typing out long variable/field names when referencing struct
>> members. We can get most of this convenience by taking the
>> address of the 'struct SCHIB' instead, avoiding triggering
>> the compiler warnings.
>>
>> In a couple of places we copy via a local variable which is
>> a technique already applied elsewhere in s390 code for this
>> problem.
>>
>> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
>> ---
>>  hw/vfio/ccw.c | 42 ++++++++++++++++++++++--------------------
>>  1 file changed, 22 insertions(+), 20 deletions(-)
> 
> I'm currently in the process of queuing this and the other three s390x
> fixes, but I'm inclined to do so for 4.1 (it feels a bit late in the
> cycle for 4.0.)
> 
> Other opinions?

IMHO it would be nice to get rid of the compiler warnings for the
release. Multiple people reviewed the patches, so I think it should
still be fine to include them.

 Thomas